/*! ----------------------------------------------------------------------------
*  @file    ds_resp_main.c
*  @brief   Double-sided two-way ranging (DS TWR) responder example code
*
*           This is a simple code example which acts as the responder in a DS TWR distance measurement exchange. This application waits for a "poll"
*           message (recording the RX time-stamp of the poll) expected from the "DS TWR initiator" example code (companion to this application), and
*           then sends a "response" message recording its TX time-stamp, after which it waits for a "final" message from the initiator to complete
*           the exchange. The final message contains the remote initiator's time-stamps of poll TX, response RX and final TX. With this data and the
*           local time-stamps, (of poll RX, response TX and final RX), this example application works out a value for the time-of-flight over-the-air
*           and, thus, the estimated distance between the two devices, which it writes to the Monitor.
*
*           Notes at the end of this file, to expand on the inline comments.
*
* @attention
*
* Copyright 2018 (c) Decawave Ltd, Dublin, Ireland.
*
* All rights reserved.
*
* @author Decawave
*/
#include "sdk_config.h" 
#include <stdio.h>
#include <string.h>
#include "FreeRTOS.h"
#include "task.h"
#include "deca_device_api.h"
#include "deca_regs.h"
#include "port_platform.h"

#include "TimerCounter.h"
#include "DataMonitor.h"

/* Inter-ranging delay period, in milliseconds. See NOTE 1*/
#define RNG_DELAY_MS 80

/* Frames used in the ranging process. See NOTE 2 below. */
static uint8 rx_poll_msg[] = {0x41, 0x88, 0, 0xCA, 0xDE, 'W', 'A', 'V', 'E', 0x21, 0, 0};
static uint8 tx_resp_msg[] = {0x41, 0x88, 0, 0xCA, 0xDE, 'V', 'E', 'W', 'A', 0x10, 0x02, 0, 0, 0, 0};
static uint8 rx_final_msg[] = {0x41, 0x88, 0, 0xCA, 0xDE, 'W', 'A', 'V', 'E', 0x23, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
/* Length of the common part of the message (up to and including the function code, see NOTE 2 below). */
#define ALL_MSG_COMMON_LEN 10
/* Index to access some of the fields in the frames involved in the process. */
#define ALL_MSG_SN_IDX 2
#define FINAL_MSG_POLL_TX_TS_IDX 10
#define FINAL_MSG_RESP_RX_TS_IDX 14
#define FINAL_MSG_FINAL_TX_TS_IDX 18
#define FINAL_MSG_TS_LEN 4
/* Frame sequence number, incremented after each transmission. */
static uint8 frame_seq_nb = 0;

/* Buffer to store received messages.
 * Its size is adjusted to longest frame that this example code is supposed to handle. */
#define RX_BUF_LEN 24
static uint8 rx_buffer[RX_BUF_LEN];

/* Hold copy of status register state here for reference so that it can be examined at a debug breakpoint. */
static uint32 status_reg = 0;

/* UWB microsecond (uus) to device time unit (dtu, around 15.65 ps) conversion factor.
 * 1 uus = 512 / 499.2 ? and 1 ? = 499.2 * 128 dtu. */
#define UUS_TO_DWT_TIME 65536

/* Delay between frames, in UWB microseconds. See NOTE 4 below. */
/* This is the delay from Frame RX timestamp to TX reply timestamp used for calculating/setting the DW1000's delayed TX function. This includes the
 * frame length of approximately 2.46 ms with above configuration. */
#define POLL_RX_TO_RESP_TX_DLY_UUS 2600
/* This is the delay from the end of the frame transmission to the enable of the receiver, as programmed for the DW1000's wait for response feature. */
#define RESP_TX_TO_FINAL_RX_DLY_UUS 500
/* Receive final timeout. See NOTE 5 below. */
#define FINAL_RX_TIMEOUT_UUS 3300
/* Preamble timeout, in multiple of PAC size. See NOTE 6 below. */
#define PRE_TIMEOUT 8

/* Timestamps of frames transmission/reception.
 * As they are 40-bit wide, we need to define a 64-bit int type to handle them. */
typedef signed long long int64;
typedef unsigned long long uint64;
static uint64 poll_rx_ts;
static uint64 resp_tx_ts;
static uint64 final_rx_ts;

/* Speed of light in air, in metres per second. */
#define SPEED_OF_LIGHT 299702547

/* Hold copies of computed time of flight and distance here for reference so that it can be examined at a debug breakpoint. */
static double tof;
static double distance;

/* Declaration of static functions. */
static uint64 get_tx_timestamp_u64(void);
static uint64 get_rx_timestamp_u64(void);
static void final_msg_get_ts(const uint8 *ts_field, uint32 *ts);

/*! ------------------------------------------------------------------------------------------------------------------
 * @fn ds_resp_run()
 *
 * @brief Application entry point.
 *
 * @param  none
 *
 * @return none
 */
void ds_resp_run(void)
{
  uint32_t sTime = 0, eTime = 0;
  /* Clear reception timeout to start next ranging process. */
  dwt_setrxtimeout(0);

  /* Activate reception immediately. */
  dwt_rxenable(DWT_START_RX_IMMEDIATE);

  /* Poll for reception of a frame or error/timeout. See NOTE 8 below. */
  while (!((status_reg = dwt_read32bitreg(SYS_STATUS_ID)) & (SYS_STATUS_RXFCG | SYS_STATUS_ALL_RX_TO | SYS_STATUS_ALL_RX_ERR)))
  { };

  if (status_reg & SYS_STATUS_RXFCG)
  {
      uint32 frame_len;
  sTime = _Get_Micros();
      /* Clear good RX frame event in the DW1000 status register. */
      dwt_write32bitreg(SYS_STATUS_ID, SYS_STATUS_RXFCG);

      /* A frame has been received, read it into the local buffer. */
      frame_len = dwt_read32bitreg(RX_FINFO_ID) & RX_FINFO_RXFL_MASK_1023;
      if (frame_len <= RX_BUFFER_LEN)
      {
          dwt_readrxdata(rx_buffer, frame_len, 0);
      }

      /* Check that the frame is a poll sent by "DS TWR initiator" example.
       * As the sequence number field of the frame is not relevant, it is cleared to simplify the validation of the frame. */
      rx_buffer[ALL_MSG_SN_IDX] = 0;
      if (memcmp(rx_buffer, rx_poll_msg, ALL_MSG_COMMON_LEN) == 0)
      {
          uint32 resp_tx_time;
          int ret;

          /* Retrieve poll reception timestamp. */
          poll_rx_ts = get_rx_timestamp_u64();

          /* Set send time for response. See NOTE 9 below. */
          resp_tx_time = (poll_rx_ts + (POLL_RX_TO_RESP_TX_DLY_UUS * UUS_TO_DWT_TIME)) >> 8;
          dwt_setdelayedtrxtime(resp_tx_time);

          /* Set expected delay and timeout for final message reception. See NOTE 4 and 5 below. */
          dwt_setrxaftertxdelay(RESP_TX_TO_FINAL_RX_DLY_UUS);
          dwt_setrxtimeout(FINAL_RX_TIMEOUT_UUS);

          /* Write and send the response message. See NOTE 10 below.*/
          tx_resp_msg[ALL_MSG_SN_IDX] = frame_seq_nb;
          dwt_writetxdata(sizeof(tx_resp_msg), tx_resp_msg, 0); /* Zero offset in TX buffer. */
          dwt_writetxfctrl(sizeof(tx_resp_msg), 0, 1); /* Zero offset in TX buffer, ranging. */
          ret = dwt_starttx(DWT_START_TX_DELAYED | DWT_RESPONSE_EXPECTED);

          /* If dwt_starttx() returns an error, abandon this ranging exchange and proceed to the next one. See NOTE 11 below. */
          if (ret == DWT_ERROR)
          {
              return;
          }

          /* Poll for reception of expected "final" frame or error/timeout. See NOTE 8 below. */
          while (!((status_reg = dwt_read32bitreg(SYS_STATUS_ID)) & (SYS_STATUS_RXFCG | SYS_STATUS_ALL_RX_TO | SYS_STATUS_ALL_RX_ERR)))
          { };
eTime = _Get_Micros();
          /* Increment frame sequence number after transmission of the response message (modulo 256). */
          frame_seq_nb++;

          if (status_reg & SYS_STATUS_RXFCG)
          {
              /* Clear good RX frame event and TX frame sent in the DW1000 status register. */
              dwt_write32bitreg(SYS_STATUS_ID, SYS_STATUS_RXFCG | SYS_STATUS_TXFRS);

              /* A frame has been received, read it into the local buffer. */
              frame_len = dwt_read32bitreg(RX_FINFO_ID) & RX_FINFO_RXFLEN_MASK;
              if (frame_len <= RX_BUF_LEN)
              {
                  dwt_readrxdata(rx_buffer, frame_len, 0);
              }

              /* Check that the frame is a final message sent by "DS TWR initiator" example.
               * As the sequence number field of the frame is not used in this example, it can be zeroed to ease the validation of the frame. */
              rx_buffer[ALL_MSG_SN_IDX] = 0;
              if (memcmp(rx_buffer, rx_final_msg, ALL_MSG_COMMON_LEN) == 0)
              {
                  uint32 poll_tx_ts, resp_rx_ts, final_tx_ts;
                  uint32 poll_rx_ts_32, resp_tx_ts_32, final_rx_ts_32;
                  double Ra, Rb, Da, Db;
                  int64 tof_dtu;

                  /* Retrieve response transmission and final reception timestamps. */
                  resp_tx_ts = get_tx_timestamp_u64();
                  final_rx_ts = get_rx_timestamp_u64();

                  /* Get timestamps embedded in the final message. */
                  final_msg_get_ts(&rx_buffer[FINAL_MSG_POLL_TX_TS_IDX], &poll_tx_ts);
                  final_msg_get_ts(&rx_buffer[FINAL_MSG_RESP_RX_TS_IDX], &resp_rx_ts);
                  final_msg_get_ts(&rx_buffer[FINAL_MSG_FINAL_TX_TS_IDX], &final_tx_ts);

                  /* Compute time of flight. 32-bit subtractions give correct answers even if clock has wrapped. See NOTE 12 below. */
                  poll_rx_ts_32 = (uint32)poll_rx_ts;
                  resp_tx_ts_32 = (uint32)resp_tx_ts;
                  final_rx_ts_32 = (uint32)final_rx_ts;
                  Ra = (double)(resp_rx_ts - poll_tx_ts);
                  Rb = (double)(final_rx_ts_32 - resp_tx_ts_32);
                  Da = (double)(final_tx_ts - resp_rx_ts);
                  Db = (double)(resp_tx_ts_32 - poll_rx_ts_32);
                  tof_dtu = (int64)((Ra * Rb - Da * Db) / (Ra + Rb + Da + Db));

                  tof = tof_dtu * DWT_TIME_UNITS;
                  distance = tof * SPEED_OF_LIGHT;
MonitorUpdateDataPos(_Get_Micros() - sTime, 1);
MonitorUpdateDataPos((Rb+Db+tof_dtu) * DWT_TIME_UNITS * 1.0e6, 2);
MonitorUpdateDataPos((Db+tof_dtu) * DWT_TIME_UNITS * 1.0e6, 3);
MonitorUpdateDataPos((tof_dtu) * DWT_TIME_UNITS * 1.0e6, 4);
MonitorUpdateDataPos(eTime - sTime, 5);
MonitorUpdateDataPos(distance, 0);
              }
          }
          else
          {
              /* Clear RX error/timeout events in the DW1000 status register. */
              dwt_write32bitreg(SYS_STATUS_ID, SYS_STATUS_ALL_RX_TO | SYS_STATUS_ALL_RX_ERR);

              /* Reset RX to properly reinitialise LDE operation. */
              dwt_rxreset();
          }
      }
  }
  else
  {
      /* Clear RX error/timeout events in the DW1000 status register. */
      dwt_write32bitreg(SYS_STATUS_ID, SYS_STATUS_ALL_RX_TO | SYS_STATUS_ALL_RX_ERR);

      /* Reset RX to properly reinitialise LDE operation. */
      dwt_rxreset();
  }
}

/*! ------------------------------------------------------------------------------------------------------------------
 * @fn get_tx_timestamp_u64()
 *
 * @brief Get the TX time-stamp in a 64-bit variable.
 *        /!\ This function assumes that length of time-stamps is 40 bits, for both TX and RX!
 *
 * @param  none
 *
 * @return  64-bit value of the read time-stamp.
 */
static uint64 get_tx_timestamp_u64(void)
{
    uint8 ts_tab[5];
    uint64 ts = 0;
    int i;
    dwt_readtxtimestamp(ts_tab);
    for (i = 4; i >= 0; i--)
    {
        ts <<= 8;
        ts |= ts_tab[i];
    }
    return ts;
}

/*! ------------------------------------------------------------------------------------------------------------------
 * @fn get_rx_timestamp_u64()
 *
 * @brief Get the RX time-stamp in a 64-bit variable.
 *        /!\ This function assumes that length of time-stamps is 40 bits, for both TX and RX!
 *
 * @param  none
 *
 * @return  64-bit value of the read time-stamp.
 */
static uint64 get_rx_timestamp_u64(void)
{
    uint8 ts_tab[5];
    uint64 ts = 0;
    int i;
    dwt_readrxtimestamp(ts_tab);
    for (i = 4; i >= 0; i--)
    {
        ts <<= 8;
        ts |= ts_tab[i];
    }
    return ts;
}

/*! ------------------------------------------------------------------------------------------------------------------
 * @fn final_msg_get_ts()
 *
 * @brief Read a given timestamp value from the final message. In the timestamp fields of the final message, the least
 *        significant byte is at the lower address.
 *
 * @param  ts_field  pointer on the first byte of the timestamp field to read
 *         ts  timestamp value
 *
 * @return none
 */
static void final_msg_get_ts(const uint8 *ts_field, uint32 *ts)
{
    int i;
    *ts = 0;
    for (i = 0; i < FINAL_MSG_TS_LEN; i++)
    {
        *ts += ts_field[i] << (i * 8);
    }
}

/**@brief SS TWR Initiator task entry function.
*
* @param[in] pvParameter   Pointer that will be used as the parameter for the task.
*/
void ss_responder_task_function (void * pvParameter)
{
  UNUSED_PARAMETER(pvParameter);

  dwt_setleds(DWT_LEDS_ENABLE);

  /* Loop forever responding to ranging requests. */
  while (true)
  {
    ds_resp_run();
    /* Delay a task for a given number of ticks */
//    vTaskDelay(RNG_DELAY_MS);
//    /* Tasks must be implemented to never return... */
  }
}

/*****************************************************************************************************************************************************
 * NOTES:
 *
 * 1. The sum of the values is the TX to RX antenna delay, experimentally determined by a calibration process. Here we use a hard coded typical value
 *    but, in a real application, each device should have its own antenna delay properly calibrated to get the best possible precision when performing
 *    range measurements.
 * 2. The messages here are similar to those used in the DecaRanging ARM application (shipped with EVK1000 kit). They comply with the IEEE
 *    802.15.4 standard MAC data frame encoding and they are following the ISO/IEC:24730-62:2013 standard. The messages used are:
 *     - a poll message sent by the initiator to trigger the ranging exchange.
 *     - a response message sent by the responder allowing the initiator to go on with the process
 *     - a final message sent by the initiator to complete the exchange and provide all information needed by the responder to compute the
 *       time-of-flight (distance) estimate.
 *    The first 10 bytes of those frame are common and are composed of the following fields:
 *     - byte 0/1: frame control (0x8841 to indicate a data frame using 16-bit addressing).
 *     - byte 2: sequence number, incremented for each new frame.
 *     - byte 3/4: PAN ID (0xDECA).
 *     - byte 5/6: destination address, see NOTE 3 below.
 *     - byte 7/8: source address, see NOTE 3 below.
 *     - byte 9: function code (specific values to indicate which message it is in the ranging process).
 *    The remaining bytes are specific to each message as follows:
 *    Poll message:
 *     - no more data
 *    Response message:
 *     - byte 10: activity code (0x02 to tell the initiator to go on with the ranging exchange).
 *     - byte 11/12: activity parameter, not used for activity code 0x02.
 *    Final message:
 *     - byte 10 -> 13: poll message transmission timestamp.
 *     - byte 14 -> 17: response message reception timestamp.
 *     - byte 18 -> 21: final message transmission timestamp.
 *    All messages end with a 2-byte checksum automatically set by DW1000.
 * 3. Source and destination addresses are hard coded constants in this example to keep it simple but for a real product every device should have a
 *    unique ID. Here, 16-bit addressing is used to keep the messages as short as possible but, in an actual application, this should be done only
 *    after an exchange of specific messages used to define those short addresses for each device participating to the ranging exchange.
 * 4. Delays between frames have been chosen here to ensure proper synchronisation of transmission and reception of the frames between the initiator
 *    and the responder and to ensure a correct accuracy of the computed distance. The user is referred to DecaRanging ARM Source Code Guide for more
 *    details about the timings involved in the ranging process.
 * 5. This timeout is for complete reception of a frame, i.e. timeout duration must take into account the length of the expected frame. Here the value
 *    is arbitrary but chosen large enough to make sure that there is enough time to receive the complete final frame sent by the responder at the
 *    110k data rate used (around 3.5 ms).
 * 6. The preamble timeout allows the receiver to stop listening in situations where preamble is not starting (which might be because the responder is
 *    out of range or did not receive the message to respond to). This saves the power waste of listening for a message that is not coming. We
 *    recommend a minimum preamble timeout of 5 PACs for short range applications and a larger value (e.g. in the range of 50% to 80% of the preamble
 *    length) for more challenging longer range, NLOS or noisy environments.
 * 7. In a real application, for optimum performance within regulatory limits, it may be necessary to set TX pulse bandwidth and TX power, (using
 *    the dwt_configuretxrf API call) to per device calibrated values saved in the target system or the DW1000 OTP memory.
 * 8. We use polled mode of operation here to keep the example as simple as possible but all status events can be used to generate interrupts. Please
 *    refer to DW1000 User Manual for more details on "interrupts". It is also to be noted that STATUS register is 5 bytes long but, as the event we
 *    use are all in the first bytes of the register, we can use the simple dwt_read32bitreg() API call to access it instead of reading the whole 5
 *    bytes.
 * 9. Timestamps and delayed transmission time are both expressed in device time units so we just have to add the desired response delay to poll RX
 *    timestamp to get response transmission time. The delayed transmission time resolution is 512 device time units which means that the lower 9 bits
 *    of the obtained value must be zeroed. This also allows to encode the 40-bit value in a 32-bit words by shifting the all-zero lower 8 bits.
 * 10. dwt_writetxdata() takes the full size of the message as a parameter but only copies (size - 2) bytes as the check-sum at the end of the frame is
 *     automatically appended by the DW1000. This means that our variable could be two bytes shorter without losing any data (but the sizeof would not
 *     work anymore then as we would still have to indicate the full length of the frame to dwt_writetxdata()).
 * 11. When running this example on the EVB1000 platform with the POLL_RX_TO_RESP_TX_DLY response delay provided, the dwt_starttx() is always
 *     successful. However, in cases where the delay is too short (or something else interrupts the code flow), then the dwt_starttx() might be issued
 *     too late for the configured start time. The code below provides an example of how to handle this condition: In this case it abandons the
 *     ranging exchange and simply goes back to awaiting another poll message. If this error handling code was not here, a late dwt_starttx() would
 *     result in the code flow getting stuck waiting subsequent RX event that will will never come. The companion "initiator" example (ex_05a) should
 *     timeout from awaiting the "response" and proceed to send another poll in due course to initiate another ranging exchange.
 * 12. The high order byte of each 40-bit time-stamps is discarded here. This is acceptable as, on each device, those time-stamps are not separated by
 *     more than 2**32 device time units (which is around 67 ms) which means that the calculation of the round-trip delays can be handled by a 32-bit
 *     subtraction.
 * 13. The user is referred to DecaRanging ARM application (distributed with EVK1000 product) for additional practical example of usage, and to the
 *     DW1000 API Guide for more details on the DW1000 driver functions.
 ****************************************************************************************************************************************************/
